U.S. soybeans screened overseas for rust

Like other soybean breeders, Grover Shannon is following Asian soybean rust with a keen eye. “I'm watching the weather and crossing my fingers,” he said from the Missouri Bootheel's Delta Center in Portageville. “We don't want it.”

With fellow researchers, Shannon recently returned from Vietnam where many U.S. soybean varieties are being screened for soybean rust. Vietnamese soybeans are hit with rust annually. While Shannon was there, rust was just beginning to show up.

“We actually saw some of the U.S. germplasm being checked, including some Missouri varieties that were flowering. Outside Hanoi, they're checking about 100 varieties we sent — 50 from northern Missouri, 50 from southern. Unfortunately, because the rust was just beginning, we couldn't tell much. Only a couple varieties looked like they might have some resistance, none from my program. We'll know more specifics when we get hard data back in the next few weeks.”

The trip came after an earlier, massive screening of U.S.-held soybean lines by the USDA and cooperating researchers.

“Folks at the University of Illinois — Monte Miles and Glen Hartman — have been on the frontlines of this. All told, I believe 16,000 varieties have been screened and assessed. The maturity groups are all the way from 000 to 10. They checked them all: soybean varieties at home in Canada to those suited for the tropics.”

After the initial screening, 800 germplasm lines appeared to have “at least some” level of resistance. Further screenings — like the work in Vietnam — will show how stout the plants are in the face of rust.

“Surprisingly, there was at least some resistance seen in varieties of each maturity group,” said Shannon. “That was welcome news.”

Besides Vietnam, research plots planted with U.S. varieties are in Brazil, Argentina and Paraguay, said Hartman, a research plant pathology associate professor at the University of Illinois. “Germplasm evaluations are easier there since rust is bound to show up. I believe we're on the right track to finding a solution for this rust. But we can't do a lot of testing (in the United States) unless there's an outbreak.”

It would be better, said Hartman, to forego an outbreak in the United States and continue research overseas.

Still, on the chance Asian soybean rust does become a problem here, Hartman said, “Some 800 lines have been distributed to a number of cooperators, primarily in the South. Most didn't get them all. However, all 800 lines will be planted in Georgia (along with Florida, the only states found to harbor the rust). They'll be planted in August under a system of field lights.”

The lights will allow the plants to grow more vegetatively.

“The idea is a wider range of maturity can be grown by providing extra light. If you grow a Group 0 in the Delta with no help, it'll be 6 to 12 inches tall. But if you provide extra light, it'll grow much taller.”

Seed from the 800 lines will be planted near the end of the normal growing season. At that time, in September and October, conditions should be cooler, wetter and more conducive to the disease.

“All our potentially resistant lines have also been sent to tropical stations to get a better reading on them,” said Hartman. “We're on track and where we need to be considering concerns about soybean rust only began a few years ago.”

Rust is difficult to breed against, according to Shannon. “There isn't a single race of the rust pathogen, but several. In other words, you could have a resistant gene that you've worked hard to develop and it'll just break down when another pathogen shows up. To counteract that possibility, the researchers mixed a bunch of isolates and screened the lines with those. From those tests, the 800 lines emerged.”

Shannon may end up breeding for tolerance because, even if successful, a resistant gene may only be good for a couple of years.

“For that reason, tolerance may be the way to go. Even with infection, the leaves will stay on and the rust doesn't develop as quickly. That might help growers keep spraying once.”

“Some of these varieties may be commercially grown, but most aren't,” said Shannon, who expects crosses to be made this summer. “Most are unadapted plant introductions that came from all over the world. A farmer could grow them, but he wouldn't want to. They aren't high-yielding. What we're most interested in are any resistant genes we can identify and put into a high-yielding variety.”

And since the lines are unadapted it will likely take “a lot longer to develop a good variety. You have to breed a lot of bad habits and vulnerabilities out of these lines. There's a lot of learning to do before we're efficient in breeding for rust. In a year or two, we'll have a better handle. We're just on the front right now.”

Are we five years from a resistant or tolerant variety? 10?

“It could be 10,” said Shannon. “But I'm more optimistic. I think with the biotechnology and ability to find certain genes, it'll be much less. Using the old system, it would definitely take a decade. But with the new biotech toolbox we have, I think it'll be closer to five years.”

A side benefit of the work in Vietnam is to “normalize relations. We can help each other. We made friends there and gave seminars on our work in Hanoi and a university in southern Vietnam. They wanted to hear about modern soybean breeding and biotechnology. They ate it up and I'm encouraged.”

Shannon said it was unlikely Vietnam would ever be a soybean competitor for the United States. “Most farms there are small — maybe 10 acres — and, for beans, they're averaging less than 20 bushels per acre. They normally grow three crops of rice a year. Mixing in a rotation with soybeans would probably help them increase rice yields.”